I am having an issue with Centos 6.9 with Hyper-V Generation-2 virtual machines on Windows Server 2016 that is related to block devices initialization.
A fresh install Centos 6.9 minimal x64 iso with latest updates and kernel 2.6.32-696.20.1.el6.x86_64 takes about 88 seconds to boot compared to a fresh install of Centos 8 minimal x64 iso that takes 7 seconds with 2.6.32-696 kernel series.
In order to get accurate time for printk messages I removed rhgb quit and added printk.time=1 to kernel line at grub.conf
As it can be seen from the attached kernel log, the kernel pauses:
For 20 seconds at:
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[ 0.694904] sr 0:0:0:1: Attached scsi CD-ROM sr0
[ 20.837103] dracut: Starting plymouth daemon
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[ 20.865167] dracut: rd_NO_MD: removing MD RAID activation
[ 51.092274] dracut: Scanning devices sda3 for LVM logical volumes VolGroup/lv_swap VolGroup/lv_root
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[ 53.465081] sr 0:0:0:1: Attached scsi generic sg1 type 5
[ 84.576559] EXT4-fs (sda2): mounted filesystem with ordered data mode. Opts:
The Centos 6.8 kernel minimal iso kernel kernel 2.6.32-642.el6.x86_64 kernel boots without any issue.
Centos 2.6.32-696 kernel series does not have that issue withand Hyper-V Generation-1 vms.
The Hyper-V Generation-2 VM is configured with 8192 MB of ram, 4 Virtual processors, one scsi contoller with a dynamic expanding 127 Gib virtual disk at position 0 and one cdrom at position 1.
I am attaching dmesg, messages and hyper vm configuration.